Field of the Invention
The present invention relates to an inkjet recording method and an inkjet recording device.
Description of the Related Art
An inkjet recording system is a recording system in which ink droplets are ejected from very minute nozzles to deposit on a recording medium, to thereby form characters or an image. This system has been recently widely used because formation of a full-color image is easier compared to other recording systems, and a high resolution image can be obtained even with a device having a simple configuration.
An ink used in the inkjet recording system requires different properties. In particular, ejection stability upon ejection of the ink from a head is an important factor that determines image quality.
An ink composition used in the inkjet recording system generally contains a colorant, a wetting agent, and water.
In the inkjet recording system, ink droplets are ejected by applying fluctuating voltage to an ink.
A meniscus is formed inside a nozzle of a head filled with the ink. In a normal (static) state, the meniscus forms a bridge from a nozzle edge toward a liquid chamber side. However, when positive pressure is applied to the ink in the nozzle due to voltage fluctuation upon ejection, the meniscus is broken, potentially leading to overflow of the ink from an outlet. Additionally, an ejected ink droplet may be torn off, or fine ink mist produced through scatter of ink droplets impacted on a substrate to be printed may deposit on a nozzle plate surface. The ink overflowed from the outlet or the ink mist deposited on the nozzle plate surface in the above described manner forms an ink puddle on the nozzle plate. When the ink puddle is brought into contact with ink droplet ejected, the meniscus turns into an asymmetric form or the ink droplet is pulled toward the ink puddle, potentially leading to deflection of an ejection direction. In an ink containing the pigment as the colorant, the pigment in the solid form is dispersed in a solvent. Therefore, when the ink deposited on the surface of the nozzle plate is dried, the pigment in the solid form adheres to the surface of the nozzle plate, eventually leading to a clogged nozzle.
Thus, in the inkjet recording system, keeping a periphery of the nozzle clean is important for ensuring stable ejection. Therefore, in order to prevent the surface of the nozzle plate from being smeared with the ink, a maintenance work has generally been performed including forming a water-repellent film onto the surface of the nozzle plate to thereby make the surface be ink-repellent and periodically wiping the surface of the nozzle plate to thereby remove the ink on the surface of the nozzle plate.
However, the water-repellent film has been known to be gradually peeled off from the nozzle plate surface by the action of the wiping.
Therefore, there has been proposed a method for improving durability of the water-repellent film in order to prevent deterioration thereof (e.g., see Japanese Patent Application Laid-Open (JP-A) No. 2010-76422).
However, the above proposed method cannot prevent the water-repellent film from being peeled off to a certain extent. Therefore, at an area at which the water-repellent film has been peeled off, image quality is deteriorated by tendency for the ink to adhere thereto, ejection disturbance, ejection deflection, and streaks on printed matter, which is problematic. Depending on properties of the ink, the nozzle plate surface has lowered ink-repellency and the ink cannot be sufficiently removed even through the wiping, which is also problematic.
For the purpose of stably ejecting an ink and providing a sharp image with little blur, there has been proposed an inkjet recording ink which contains self-dispersing colorant particles, and which has the static surface tension of 30 mN/m to 50 mN/m, the advancing contact angle of 65° or more and the receding contact angle of 55° or more on the nozzle plate surface of the recording head, and a difference between the advancing contact angle and the receding contact angle of 20° or less (e.g., JP-A No. 2003-277651).
However, in this proposed ink, ejection stability cannot be ensured in the case of low static surface tension, which is problematic.
JP-A No. 2011-62821 proposes a method for improving ejection reliability by shortening an entire drive waveform within one printing cycle to thereby increase the printing speed, and forming an ejection pulse including a waveform element corresponding to size of ink droplets.
JP-A No. 10-34941 proposes an inkjet recording head which allows a pigment ink located on a surface of a nozzle plate to be fully removed with a wiping unit by defining a difference between the advancing contact angle and the receding contact angle of the pigment ink on the surface of the nozzle plate in the inkjet recording head.
Japanese Patent Application Publication (JP-B) No. 04-35344 proposes an inkjet recording head which allows an ink to jet accurately and stably by defining the advancing contact angle and the receding contact angle of the ink on a surface of a nozzle plate.
JP-A No. 04-241948 proposes an inkjet recording head which has a high liquid-repellency by defining a relationship (the receding contact angle of the ink) between the inkjet recording head and a liquid-repellent treatment agent for liquid-repellent treating an end face of the inkjet recording head provided with an ink outlet.
However, these proposals have a problem that a water-repellent film formed on a nozzle plate surface is gradually peeled off under the influence of the wiping.
Therefore, in the present, there is a need to provide an inkjet recording method which allows an ink having a low static surface tension and a small receding contact angle to eject stably and which achieves an excellent image even when a water-repellent film formed onto a surface of a nozzle plate is deteriorated.